Double Mantle Plume Upwelling—A Possible Formation Mechanism of Beta Plateau and Devana Chasma,Venus

Ning Ding,Zuoxun Zeng,China University of Geosciences,Wuhan,430074,China NingDing.eagle@gmail.com Introduction:Venus represents a‘one plate planet’[1],and the uplift,fractures and volcanism in Beta Regio on Venus are considered to be formed by lithosphere uplift driven by a hot plume[2]. Based on the double peaking saddle landform,we suggest the tectonic pattern of double mantle plume upwelling to interpret the formation mechanism of Beta Plateau and Devana Chasma.We take a physical modeling to validate this possibility. Model:There is no ductile shear in Venus[3],so we use quartz sands to simulate the crust of Venus.We use two wood stickes 1.5cm in diameter rising from the rubber canvas slowly and straight till about half of the model,then falling down slowly and straight.The base is a hard rubber plate,in the center of which,there are two holes 3cm in diameter,and the distance between them is 5cm.The holes are covered by rubber canvas.We use the quartz sands in colours of white, red and black with particle size of 70 mess as the model materials. Result:Fig.1:At the beginning of the wood stickes upwelling,only fine radial cracks are formed above the upwelling from central to outside.With the upwelling continue,surface energy of the fine radial cracks increase and make the cracks unstable,finally,the fine radial cracks connect each other and form a fracture zone.And then the two mantle plume downwelling,the fracture zone is developed to form a chasma at the end. Fig.2:The four profiles all form reverse faults outside and normal faults inside.But the difference is the faults in the middle of the chasma goes deeper than others.It is the pattern of Beta Plateau where the tectonic rising is cut by Devana Chasma zone in the topographic features. Fig.3:From the tow fig., we can see two points similar:a.the elevation is high and distribution area is large around the area of two upwelling and it is high around the area of chasma,but the distribution area is small;b.both of them shows saddle shape and two highland connectting bya chasma. Discussion:Based on the‘Geology Map of V-17’,two highlands of Northern part of Devana Chasma,but the material Unit of North and South highland are different.The material Units of North highland are the oldest unit tt and t,the material Unit of South highland is pl and the material Unit of rift is r are both the youngest unit.From the Magellan SAR mosaic[5],we can clearly see Devana Chasma cut the material Unit of tt and pl.So the two highlands of Northern part of Devana Chasma are simultaneous formed.The younger material Unit of South highland of Northern part of Devana Chasma is because of the volcanic eruption of Theia Mons. Conclusion:The physical modeling validates the model of the double plume upwelling is a possible explanation. Acknowledgements:This research was supported by the National Teaching Bases For Geology(CUG)foundation funded. References:[1]I.López,Icarus2008[2]A.T.Basilevsky,Icarus2007[3]J.C.Aubele,2009,LPSC[4]A.V.Vezolainen,2003,Journalofgeophysicalres5earch[5]http://planetarynames.wr.usgs.gov/images/v17_comp&v29_comp.pdf Fig.1 Fig.2 Fig.3a,3b